What is JAVA ?
Java is a high level , popular, object oriented programming language , it’s purpose is : WORA (Write Once , Run Anywhere) , that means compiled java code can run in any plateform without the need to recompile it again
Java Features
- Object Oriented : Abstraction , encapsulation , polymorphism , inheritance , object,Class.
- Platform Independant (interpreted also) : Java compiler compile code into byte code this byte code run by JVM on any platform.
- Easy to learn / simple: if you understand OOP , and if you already know about c and c++ , java inherit features from these languages and remove its complex feature like pointers , operator overloading ,multiple inheritence and explicit memory allocation (provides garbage collection).
- Secure : a developer is not required to interact with memory or operating system , Java provides automatic garbage collection so developer don t have to worry about memory leaks / management …
- Architectural neutral : jre handles automatically java byte code execution on any processor
- Portable : the same code executed on any platform
- Robust : compile-time error check ,strict type checking and runtime error handling
- Multithreading : multiprocess, thread handle , deadlock handle …
it enables you to run multiple threads at the same time. - High performance : JIT(just in time) compiler improve performance
- Distributed : developping internet based applications.
- Dynamic : more dynamic than c and c++ because it can adapt to an evolving environment.
Java’s release date
1995
Java’s original name
oak
Java Platforms (editions)
- JAVA SE ( java standard edition ) : develop and deploy portable code for desktop and server environments
- JAVA EE ( java enterprise edition ) : to develop web apps
- JAVA ME ( java micro edition ) : to develop mobile apps
- JavaFx : to develop light-weighted user interface for rich internet apps.
multitasking vs multiprocessing vs multithreading
multitasking : the ability of OS to execute multiple task simultaneously . there two type of multitask :
*multiprocessing : you can run multiple process and programs that doesn t share the same cpu and memory space (more isolated than threads) which make multiprocess a resource-intensive . it s good for CPU-BOUND where each process run in parallel on a different CPU cores.
*mutithreading : run mutliple thread with the same memory space and cpu (single process) which make communication / switch between threads more easier and lightweight.
=> Java have built-in support multihreading with Thread Class and Runnable Interface
BUT doesn t have built-in support multiprocessing , you can run java applications separately or use libraries for inter-process communication (IPS) if needed.
C++ Features
- middle level language : it can be used for systems development and large-scale app consumer.
- Execution speed : C++ is a compiled language and use procedures extensively.Garbage collection and dynamic typing and other modern features impede program execution.
- Object Oriented Programming : Growing code makes procedural code harder to handle. that’s the key advantage between c and C++.
*Extensive Libraries : C++ has a vast libraries like 3rd party which make development faster
Java vs C++
- platform independent + interpreted + compiled :
jAVA : can run on any platform (because java interpreted compiled)
C++ : can t (only compiled) - Memory management :
Java : GC manage it automatically
C++ : manage it manually (with help of ‘new’ and ‘delete’).
*Libraries:
Java:don t support it directly, but we can configure it using 3rd party libraries.
C++:support direct system library calls.
*Multiple inheritance:
JAVA: support only single inheritance.
C++ : support multiple inheritance because of the ‘virtual’ keyword
*Mutithreading:
JAVA: support it.
C++:don t , but can by using 3rd party libraries.
*Pass by value/reference :
Java : Java support pass by value only , both in primitive type and also in object reference.
C++: support pass by value , and pass by reference using the pointer &.
What is difference between pass by reference and pass by value ?
On Pass by Value , we pass a copy of the value.
But on Pass by Reference we pass the same reference.
JVM Architecture
- Class Loader:
has 3 types : Bootstrap , Extension , Application Class Loader.
JVM manages the process of loading,linking and initializing classes and interfaces in a dynamic manner.
During the loading process, JVM find binary representation of a class and creates it.
In the linking process, loaded classes combined with run-time state of JVM so they can be executed during initialiazing phase.
During initializing, execution of linked classes
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JVM Memory/Runtime Data Areas: - Method Area:
- JVM Language Stacks:
- Native Method Stacks:
- PC (Program counter) Register:
- Heap:
___________________________________________ - Execution Engine : comprises GC , Compiler JIT and Interpreter.
=>JIT Compiler : is a part of JRE and it compiles byte code to machine code at runtime. - Native Method Interface :
- Native Method Libraries : collection of c and c++ libraries which are essential for execution.
What JDK, JRE and JVM ?
- JDK (java development kit) : it include all the tools ,executables and binaries for compile , debug and execute a java program.
It is platform dependent (there are different installers for windows, mac, unix)
JDK contains JRE and JVM.
the version of JDK define Java version
______________________________ - JRE (java runtime environment): it is JVM’s implementation , it is responsible for code execution
platform dependent
_____________________________
*JVM (java virtual machine): it is a specification / something abstract.
Convert byte code to machine code and can also run code.
platform independent
How much variables java has ? and what is it ?
- Local variables: are always inside a block ( constructor , method … ), created in block , destroyed after skip block.
no default value.
can t use access modifiers
*static/class variables: outside block, inside class , have a default value
can access without creating a new object (className.varName)
created when program start , destroyed when program end
there are only one class variable copy per class , regardless of how many objects we create from it.
*Instance variables (non-static variables):outside block, inside class , have a default value.
created when object created , destroyed when object destroyed
How much modifiers java has ? and what is it ?
- Access Modifiers:
-default : Visible to package , no modifiers required
-public : visible to world
-private : visible to class only
-protected : visible to all subclasses and package - Non-access modifiers: final, abstract, strictfp
Java Data types
- Primitive:int, long , short, float , double , byte …
- Object/Reference
Java type casting (type conversion)
- Widening: also implicit type casting where compiler automatically cast a smaller type to a larger type.
- Narrowing: also explicit type where programmer manually cast type from large to small.
Java Generics
Are methods and classes that we use for different types without writing it again.
What is difference between Functional programming vs OOP ?
=> In functional programming we focus on pure functions ,state immutability(stateless),and using features like lambdas and stream for declarative logic.
It is used when we have parallel operations and data processing
=> For OOP , we focus on using object and classes ,mutable state(stateful) and concepts like abstraction , polymorphism , encapsulation , inheritance + imperative logic
=> it is used for data modeling and need of principes like inheritance …
